We will send your comments, along with a link to this page, to the appropriate project members. Your information will not be kept in our records or used for any other purpose than to send the message. Fields marked with an * are required.

Name:*

Organization:*

Email:*

Message:*

Security Code:*(Please enter the code in the box provided. Thisprotects the form fromabuse.)

Within This Page

Introduction

The term "materials" refers to all the physical substances that are assembled to create the interior and exterior of a building. Today most buildings are constructed from a multitude of materials, each with very specific functional demands and complex assembly requirements. For instance, an exterior wall assembly contains materials that keep the rain and wind out, thermally insulate the inhabitants from exterior temperatures, structurally support the building and the associated enclosure system, and provide desired interior and exterior finishes. In addition, windows, doors, vents, and other apertures connect to the interior and exterior of the building. The list could go on, but this example should serve to illustrate the complexity and importance of the material selection process in building design. These decisions should be based on a number of carefully considered issues as described below, including symbolism, appropriateness, physical properties, and technique.

Description

Fig. 1. Wood quoins symbolize stone

A. Symbolism

Particular materials carry specific connotations within cultures and regions. Terms such as natural or artificial, eternal or ephemeral, austere or opulent, describe a few such associations. We often refer to the enduring qualities of stone, or the ephemeral nature of glass or paper. In some cases, the material associated with a desired symbolic expression is not available or too costly, and another material is substituted to replicate that material and achieve the desired effect. Mount Vernon, the home of George Washington, illustrates this situation. The symbolic solidity of stone was imitated in the carved and painted wooden construction of the house exterior. See Fig. 1.

B. Appropriateness

There are three primary areas that must be evaluated in selecting appropriate materials and assemblies.

Climate is one of the most important factors to consider in material and assembly selection. Too often we see buildings that have not taken local environmental conditions into consideration, by either replicating the same prototypical design from Alaska to Arizona, or by designing a building for a specific site that ignores climatic issues. The result is a building that performs poorly—failing to keep inhabitants comfortable without excessive energy expenditures and near complete reliance on mechanical systems to rectify poor construction decisions (see High Performance HVAC). Materials also must be compatible with specific regional and local cultural and aesthetic conditions. For example, the Southwestern adobe and flat roof residential construction would not export well to New England, where the widespread use of wood framing, clapboard siding, and pitched roofs is climatically appropriate, as well as culturally embraced.

Applicability of Material to Occupancy and Size of Building, Including Durability, Structural, and Fire Protection Requirements

Material choices are often legally limited by the building type and size, in order to protect public health, safety, and welfare. For instance, a detached single-family house has far fewer limitations than a high-rise office building or a federal courthouse, from which hundreds of inhabitants must be evacuated in case of emergency. In general, buildings with large occupancy numbers (especially assembly occupancy such as theaters, lecture halls, and restaurants) and greater enclosed square footage require more fire-resistant construction and more complex fire protection systems. Another concern is the added wear and tear on a densely inhabited and intensely used building, such as a public school or hospital, where material durability is a major concern.

Where did this material come from? Ideally materials should be obtained from renewable sources, such as wood harvested from sustainably managed old growth forests.

How was it processed or fabricated? The energy and resources expended in material preparation, sometimes termed "embodied energy," must be taken into account.

How did it arrive on-site? Transportation impacts and expenses should be minimized, with locally available materials often making a better choice than those imported from afar. For example, if building in Vermont, select locally quarried stone rather than specifying imported marble from Italy.

How long will it last? How will it eventually be disposed of? Materials should be selected with durability and life span in mind. Recycled materials should be chosen when possible. Consider designing easily dissembled buildings that may be reused and recycled in the future.

How will this material impact the environment while in place? For example, many paints, carpets, acoustic ceiling tile, vinyl flooring and wallcoverings, and adhesives contain volatile organic compounds (VOC's). Avoid using materials embodying VOC's, and select low toxicity building materials to avoid off-gassing after construction completion.

How can the use of a particular material minimize construction waste? Choose construction materials that don't have a lot of by-products. For instance, building with reusable formwork for cast-in-place concrete construction avoids plywood and wood formwork waste on-site.

See the Sustainable design objective section for a comprehensive discussion of sustainable building design, including fundamental principles, implementation strategies and sustainable building material links.

C. Physical Properties

A number of physical properties must be taken into account in the material selection process. While certain properties are inherent to the material and unchangeable, other qualities can be determined in the fabrication or finishing process. The following outline lists only primary considerations, since each material possesses a unique combination of properties.

Strength

Material strength quantifies resistance to compression, tension, and other types of loading on a given material. For instance, masonry performs most effectively as a load-bearing or compressive material, while steel is a more suitable choice for greater spanning and tensile requirements.

Mass and Thickness

After an initial material selection is made, the dimensional thickness of each material must be based on requirements for durability, strength, and aesthetic considerations.

Physical and Visual Density

Often a particular tactile density is desired, ranging from heaviness to lightness in degrees of opacity, translucency, or transparency. See Figs. 2 and 3.

Texture

Many materials may be finished to different textures, either during off-site production or while finishing materials on-site. Smooth to rough, soft to hard, and a range of surface finishes—matte, satin, polished, and so on—are possible. See Fig. 4.

Color

Selection of a building color palette must consider the surrounding context, as well exterior and interior light qualities under which the colors will be viewed. The cool diffused light of Seattle will render colors quite differently than the hot clear light of Phoenix. Colors may be light absorptive or light reflective, warm or cool, while the palette may be monochromatic or polychromatic. See Figs. 5 and 6.

Temperature

The tactile qualities of architecture are of utmost importance, especially those surfaces that building inhabitants touch on a regular basis, such as door hardware, work surfaces, and floor materials. Metal surfaces quickly register temperature change, while stone more slowly absorbs ambient temperatures and retains temperature much longer. Thus, material thermal conductivity is an important consideration in the comfort of occupants.

Pattern

Material patterning must be designed at two scales: the individual elements themselves, such as bricks or glass panes, and the composition of these elements into larger assemblies. For example, at the individual element scale the inherent patterning of wood grain or stone marbling must be considered. The creation of larger patterns occurs when the material is assembled into building facades. See Figs. 7 and 8.

D. Technique

Fig. 9. Prefabricated sunshading

The methods of material fabrication and assembly are a complex aspect of the construction process. Technique includes the fabrication process, the detailing of how materials and systems are joined and erected, and the craft employed to execute the work.

Fabrication

Fabrication refers to how a material was created, processed, and assembled. Fabrication techniques range from handcrafted to mass produced to prefabricated. Materials carry traces of their making and assembly that can be used to create surface modulation and richness. See Fig. 9.

Fig. 10. Exposed steel truss

Detail

Construction details determine how individual material elements or systems are joined. Common methods of joinery include various types of mechanical fastening (nails, bolts, rivets...), welding, adhering, and so on. Construction details should relate to the overall architectural intentions of a building. Attention to detail is evident in a well-resolved and finely executed building, such as the elegant assemblage of wood and concrete systems in Fig. 10.

Craft

The quality of design and construction workmanship is crucial to the success and longevity of a project. The employment of well-trained and experienced trades people is the best way to assure a high level of building craft. See Fig. 11.

Weathering

The passing of time has an immense impact on the appearance and life span of building materials. Thus, future weathering must be carefully considered during material selection, building detailing, and construction. See Fig. 12.

Application

The application of particular building materials and systems is discussed in numerous sections of the Whole Building Design Guide. Particularly refer to the Products and Systems category and the Sustainable design objective sections for more detailed information.

Relevant Codes and Standards

Building codes limit the allowable materials for a particular building, based on building occupancy type and zoning considerations. Occupant life safety is the primary concern of such codes, which limit material combustibility, flame spread rating, and smoke toxicity. In some jurisdictions, Historic District guidelines or other visually-based design guidelines may specify allowable exterior materials, color selection, and other aesthetic considerations including style.